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Related Concept Videos

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

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In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
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Aromatic Hydrocarbon Anions: Structural Overview01:18

Aromatic Hydrocarbon Anions: Structural Overview

3.5K
Neutral hydrocarbons like cyclopentadiene with an odd number of carbon atoms and one intervening CH2 group in the ring are not aromatic. Cyclopentadiene with 4 π electrons does not satisfy the 4n + 2 π electron rule. Additionally, the intervening CH2 group is sp3 hybridized and lacks a vacant p orbital, thereby interrupting the overlap of p orbitals in a continuous manner and preventing the delocalization of π electrons throughout the ring.
Due to the absence of continuous...
3.5K
Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)01:30

Nucleophilic Aromatic Substitution: Addition–Elimination (SNAr)

4.6K
Nucleophilic substitution in aromatic compounds is feasible in substrates bearing strong electron-withdrawing substituents positioned ortho or para to the leaving group. The reaction proceeds via two steps: the addition of the nucleophile and the elimination of the leaving group.
The reaction begins with an attack of the nucleophile on the carbon that holds the leaving group. This results in the delocalization of the π electrons over the ring carbons. The resonance interaction between...
4.6K
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

3.6K
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group...
3.6K
Criteria for Aromaticity and the Hückel 4n + 2 Rule01:20

Criteria for Aromaticity and the Hückel 4n + 2 Rule

12.5K
Like benzene, cyclobutadiene and cyclooctatetraene are cyclic compounds with alternate single and double bonds. However, their chemical behavior differs from benzene, as they are unstable and not aromatic. So, what are the structural characteristics of unsaturated compounds categorized as aromatic?  
For the first time, Eric Hückel, a German chemical physicist, derived a set of structural features for a compound to be classified as aromatic. This is now known as Hückel’s rule or the 4n +...
12.5K
Electrophilic Aromatic Substitution: Overview01:16

Electrophilic Aromatic Substitution: Overview

13.3K
In an electrophilic aromatic substitution reaction, an electrophile substitutes for a hydrogen of an aromatic compound.
13.3K

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Related Experiment Video

Updated: Jan 2, 2026

Resonance Fluorescence of an InGaAs Quantum Dot in a Planar Cavity Using Orthogonal Excitation and Detection
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Resonance Fluorescence of an InGaAs Quantum Dot in a Planar Cavity Using Orthogonal Excitation and Detection

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Through-space aromatic character in excimers.

Vishnu Vijay1, Meera Madhu, Remya Ramakrishnan

  • 1School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, (IISER TVM), Maruthamala P. O., Vithura, Thiruvananthapuram, Kerala 695551, India. mahesh@iisertvm.ac.in.

Chemical Communications (Cambridge, England)
|December 6, 2019
PubMed
Summary

This study provides the first theoretical evidence of aromatic character in triplet state excimers of common aromatic molecules. This finding reveals new possibilities for understanding excited-state processes in complex aromatic systems.

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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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Last Updated: Jan 2, 2026

Resonance Fluorescence of an InGaAs Quantum Dot in a Planar Cavity Using Orthogonal Excitation and Detection
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Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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Area of Science:

  • Photochemistry
  • Theoretical Chemistry
  • Physical Chemistry

Background:

  • Aromaticity is a key concept in chemistry, but its role in excited states, particularly excimers, is not well understood.
  • Excimers are fundamental entities in excited-state chemistry with broad applications.

Purpose of the Study:

  • To investigate the presence and nature of aromaticity in triplet state (T1) excimers.
  • To explore the concept of through-space aromaticity in excited-state molecular complexes.

Main Methods:

  • Utilized multiple theoretical aromaticity descriptors, including magnetic, electronic, and geometric criteria.
  • Calculated chemical shifts and induced current densities to analyze electronic properties.

Main Results:

  • Presented the first theoretical evidence for excited-state through-space aromatic character in triplet state excimers of benzene, naphthalene, and anthracene.
  • Demonstrated the existence of transannular π-electronic currents within these excimers.

Conclusions:

  • The findings suggest that aromaticity can manifest in excited states through space, challenging previous understandings.
  • Opens avenues for research into singlet excimers and the role of aromaticity in photoexcited supramolecular systems.